The present invention pertains to bolt assemblies, and more particularly pertains to buffered bolt assemblies, of the type used in automatic weapons.
In conventional buffered bolt assemblies, a relatively massive bolt is mounted on a bolt carrier in such a manner as to be both rotatable about its own axis and slidable fore and aft (axially) relative to the bolt carrier. Typically, the bolt has one or more cam pins on it which engage cam guides formed in the bolt carrier, the cam guides being so shaped as to allow the bolt to slide axially only within certain limits and to cause the bolt to rotate about its axis in a predetermined fashion as it slides axially. Thus, the bolt has two extreme positions relative to the bolt carrier: a first position, in which it has a first rotational orientation and a first axial position that is relatively far forward relative to the bolt carrier, and a second position in which it has a different rotational orientation and is farther to the rear relative to the bolt carrier. A buffer, which is spring-biased forward, is disposed to the rear of the bolt and bolt carrier.
The operational cycle of the conventional buffered bolt assembly includes a recoil stroke, in which the bolt carrier is forced to the rear by the recoil of the weapon, and a forward stroke, in which the bolt carrier is driven forward by the spring bias of the buffer. During the recoil stroke, the spent cartridge of a round that has just been fired is ejected, and on the following forward stroke the bolt engages a fresh cartridge that has in the meantime been fed into the chamber position and moves the new cartridge into position for firing. At the end of the forward stroke, inertia carries the firing pin, which is mounted on the bolt carrier, forward to fire the round, completing the cycle. When the bolt carrier is at its forwardmost point, the bolt is in the first, or forward, position described above relative to the bolt carrier. As the bolt carrier begins its rearward movement at the beginning of the recoil stroke, the bolt remains axially stationary in the weapon until the bolt carrier has moved sufficiently far aft to bring it and the bolt into the second relative position described above. This relative movement of the bolt and bolt carrier causes the bolt to rotate, unlocking the bolt from the end of the barrel and bringing a notch or the like on the bolt into axial and rotational alignment with a latch device provided on the bolt carrier. The latch device is biased to engage the notch when this alignment occurs. Thus, at the end of the first part of the recoil stroke, the bolt has been unlocked from the forward end of the weapon chamber and has been secured relative to the bolt carrier by means of the latch device, and by means of the cam pins and cam guides. During the remainder of the recoil stroke, the bolt and bolt carrier move rearward as a unit until the bolt carrier impacts the spring-biased buffer, which decelerates the bolt carrier to a stop. Because of the latch and cam pin connections, the bolt is also brought to a stop simultaneously with the bolt carrier. The compressed spring of the buffer then drives the bolt carrier and the bolt forward for the forward stroke of the cycle. The bolt, as stated above, grasps the newly fed-in cartridge and drives it home into the firing position. The bolt carrier continues moving forward after this has occurred, forcing the bolt to rotate into locking engagement with the back end of the barrel for firing. At the end of the forward stroke, the firing pin, which is supported on the bolt carrier, is carried forward by its inertia against the cartridge, firing the round.
As will be clear from the foregoing description, the latch device and the cam pins are subjected to a very heavy load at the end of the recoil stroke and the beginning of the forward stroke, when the bolt carrier is suddenly brought to a stop and then is propelled forward by the buffer. This tends to shorten the life of the latch device and/or the cam pins, and requires the use of extra-strong designs for these elements.